US3612724A

US3612724A - Hydraulic apparatus

Info

Publication number: US3612724A
Application number: US884998A
Authority: US
Inventors: John Denis Smith
Original assignee: Boulton Paul Aircraft Ltd
Current assignee: Boulton Paul Aircraft Ltd
Priority date: 1968-12-14
Filing date: 1969-12-15
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12

Abstract

A swash plate pump in which the swash plate is adjustable in accordance with the pump delivery pressure so that piston stroke reduces as delivery pressure increases. A pair of piston-andcylinder servo units are provided to act oppositely on the swash plate, one of these servo units being fed with liquid at pump delivery pressure and the other servo unit being fed with liquid either at pump delivery pressure or a lower pressure depending on the position of a control valve. The control valve is contained within the said other servo unit and is subjected at one end to pump delivery pressure and at its opposite end to the load of a compression spring whereby to take up a position depending on pump delivery pressure. The pressure of liquid fed to the said other servo unit will be adjusted accordingly and the angle of the swash plate will be adjusted by the one or the other servo unit in accordance with pump delivery pressure.

Description

United States Patent John Denis Smith Wolverhampton, England [21] Appl.No. 884,998

[72] Inventor [22] Filed Dec. 15, 1969 [45] Patented Oct. 12, 1971 [73] Assignee Boulton Paul Aircraft Limited Wolverhampton, Stafford, England [32] Priority Dec. 14, 1968 33] Great Britain [54] HYDRAULIC APPARATUS Primary ExaminerLeonard H. Gerin Attorney-Young & Thompson ABSTRACT: A swash plate pump in which the swash plate is adjustable in accordance with the pump delivery pressure so that piston stroke reduces as delivery pressure increases. A pair of piston-and-cylinder servo units are provided to act oppositely on the swash plate, one of these servo units being fed with liquid at pump delivery pressure and the other servo unit being fed with liquid either at pump delivery pressure or a lower pressure depending on the position of a control valve. The control valve is contained within the said other servo unit and is subjected at one end to pump delivery pressure and at its opposite end to the load of a compression spring whereby to take up a position depending on pump delivery pressure. The pressure of liquid fed to the said other servo unit will be adjusted accordingly and the angle of the swash plate will be adjusted by the one or the other servo unit in accordance with pump delivery pressure.

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mmv wm mm/ mmmmwwmm w HYDRAULIC APPARATUS This invention relates to hydraulic apparatus and more particularly it relates to a variable stroke hydraulic pump.

In accordance with the present invention a variable stroke hydraulic pump comprises a rotary cylinder block, pump pistons extending from cylinders in the block to engage a cam member such that the pistons reciprocate during block rotation, a pair of servo piston and cylinder units arranged to act by hydraulic pressure oppositely on the cam for moving the cam in the sense to vary piston stroke, a hydraulic connection from the pump delivery extending directly to one servo piston, a hydraulic connection from the pump delivery extending to a pilot valve in the second servo piston and a spring acting on the pilot valve in opposition to the force developed by pump deliverypressure whereby the pilot valve assumes a position in accordance with pump delivery pressure to connect the pump delivery pressure or a lower pressure to act on the second servo piston to adjust the cam to a position in accordance with the position assumed by the pilot valve.

The cylinders in the block may be parallel or inclined to the block rotation axis and the cam may be a swash plate.

Preferably both servo units are located at equal distances from the tilt axis of the swash plate and the area of the first servo piston is smaller than the area of the second servo piston.

One embodiment of the invention will now be particularly described with reference to the accompanying drawings, in which FIG. 1 is a diagrammatic view of an integrated unit including the variable stroke pump,

FIG. 2 is a cross section through the variable stroke pump, and

FIG. 3 is a cross section through an accumulator forming part of the integrated unit.

The described embodiment is intended for use on an aircraft as a hydraulic package control i.e. an integrated unit comprising electric driving motor, hydraulic pump, hydraulic ram, liquid reservoir and control valve whereby the package may be located at an appropriate place for example in the wing of the aircraft for operation of a control surface, the power supply being through electric cables to the motor and the control being by means of a convenient linkage system to the control valve.

In the embodiment, the hydraulic pump comprises a swash plate pump I mounted within a finned reservoir 2. An extension 3 of the reservoir locates a reduction gear 4 and provides a mounting flange 6 for a high-speed electric motor 7. The hydraulic motor is secured to the extension 3 of the reservoir, and takes the form of a cylinder 8 containing a double acting piston 9.

An accumulator structure 11 is also secured to the extension 3 of the reservoir.

The hydraulic pump comprises a rotary cylinder block 12 having cylinders 13 extending parallel to the rotation axis and pistons 14 in the cylinders which extend from one end of the cylinder block to engage a swash plate 15. The swash plate is pivotally mounted by trunnions for tilt movement in order to vary the effective stroke of the pistons in their cylinders during rotation of the cylinder block. The block is mounted for rotation on a valve 16 having a pair of main ports 17 and 18. The port 17 is the inlet port to the pump and the port 18 is the high-pressure delivery port.

In order to adjust the angular setting of the swash plate a pair of piston and cylinder servo units 19 and 21 are provided. These two servo units are secured to the mounting structure 22 by which the whole pump is carried within the reservoir 2 and are equidistantly spaced from the axis of the swash plate trunnions 10. The servo unit 19 is a simple piston and cylinder unit receiving high-pressure liquid directly from the high-pressure delivery port 18 through a passage 23 and acting directly on the swash plate 15 through a connecting rod 20.

The servo unit 21 is mounted on the opposite side of the pump to the servo unit 19 and basically comprises a piston 24 slidably mounted in a cylinder 25. A connecting rod 30 connects the piston 24 to the swash plate 15. The thrusts exerted on the swash plate 15 by the two connecting rods 20 and 30 generate opposing torques on the swash plate about the axis of the trunnions 10. The cross-sectional area of the piston 24 over which liquid may act is larger than the cross-sectional area of the piston in servo unit 19.

A cylindrical pilot valve 27 is slidably mounted within the piston 24, a land 28 on the pilot valve controlling access of liquid into a working space 26 within which liquid may act on the piston 24 to urge it towards the swash plate. For this purpose a waisted portion 29 of the pilot valve is adapted to connect a pressure port 31 or a reservoir port 32 to the working space 26 depending on the axial piston position of the pilot valve in the piston. At one end the pilot valve carries a small plunger 33 which reacts directly against the piston 24, the pressure liquid having access to the one end of the plunger 33 so that the pressure of liquid will tend to urge the pilot valve to the left as seen in the drawing. The delivery port 18 of the pump is connected by a passage not shown to a grooved zone 34 around the piston 24 from which the liquid has access both to the port 31 and to the plunger 33.

The end of cylinder 25 remote from the swash plate contains a compression spring 35 on which the pilot valve 27 is arranged to react through the medium of a spring cap 36 whereby the axial position taken up by the pilot valve depends on the endwise force exerted on the pilot valve by virtue of liquid pressure acting over the area of plunger 33 in opposition to the compression force exerted by the spring. The spring is a conventional coiled spring having a substantial rate so that for each value of delivery pressure within a working range there is a corresponding position for the pilot valve.

In operation of the pump, rotational drive is applied to the shaft 37 which in turn rotates the cylinder block 12 thus causing the pistons 14 to reciprocate in their cylinders whereby liquid enters port 17 from the reservoir to be delivered as liquid at pressure from the port 18. initially such liquid at pressure will be supplied to both servo units 19 and 21 and the servo piston 24 by virtue of its greater area will hold the swash plate 15 at its maximum inclination. As delivery pressure rises to a particular value the force exerted on the pilot valve 27 will cause it to move against the load of the spring 35. Such movement of the pilot valve will connect low pressure to the working space 26 and the swash plate 15 will be moved about its trunnions 10 by the force exerted by servo unit 19 until the connection to working space 26 is again closed by the land 28 of pilot valve 27. Thus there is a unique relation between the pressure at the delivery port 18 and the angular setting of the swash plate.

Liquid is arranged to enter the port 17 from the reservoir through a filter 38.

Liquid delivered by the pump is arranged to pass through passages (not shown) in the portion 3 of the reservoir case to a control valve 39 which will direct the liquid at pressure to one end or the other of the cylinder 8 so that movement of the piston 9 is in accordance with the position selected for the control valve 39. Conventional feedback linkage may be provided in between the control valve 39 and the control device operated by the piston 9.

The accumulator assembly 11 supported from extension 3 comprises a pair of coaxial cylinders 41 and 42 internally separated by a flange 43. The left hand end of cylinder 41 is closed by a cap 44 formed as an extension from the portion 3 of the reservoir. The right-hand end of the cylinder 42 is closed by a cap 45. Within cylinder 41 a free piston 46 is slidably mounted. The left-hand end of cylinder 41 forms the high-pressure accumulator and is connected through a passage 47 with the delivery pressure from the port 18 of the pump. The right-hand end of the cylinder 41 is filled with an inert gas such as nitrogen under high pressure, the pressure being substantially equivalent to the delivery pressure from the pump. A piston rod 48 extends through a suitably sealed opening in the flange 43 from the cylinder 41 to the cylinder 42 and in cylinder 42 is connected to a piston 49. The piston rod 48 and piston 49 together form a differential piston. The cylinder 42 forms the low-pressure accumulator. The passage 51 extending from the right-hand end of the cylinder 42 connects to the reservoir 2. The left-hand end of cylinder 42 is vented to atmosphere. The high pressure within cylinder 41 exerts an endwise force on the rod 48 which is transferred to the piston 49 to act on the liquid in the right-hand end of cylinder 42. Thus the pressure of the liquid in the right-hand end of cylinder 42 will be smaller than the high pressure in cylinder 41 in proportion to the-areas of the piston 49 and piston rod 48. For example it may be arranged that the pressure within cylinder 42 is one tenth of the pressure within cylinder 41. An indicator rod 52 is secured to the piston 49 and extends through a suitably sealed opening in the end cap 45 to form an external indicator of the quantity of liquid contained within the low-pressure accumulator. As liquid escapes from the system by leakage, the indicator rod 52 will move further and further from the end cap 45, and in service regular inspection will establish the amount by which the indicator rod projects thereby to indicate whether or not it is necessary to put more liquid into the reservoir. Liquid may be fed into the reservoir through a filler cap 53 mounted in a screw threaded filling hole 54 on the reservoir. The cap 53 may contain a spring loaded nonretum valve 55 arranged to vent liquid from the interior of the reservoir if the pressure should become excessively high. The extension 3 also includes a highpressure relief valve 56 arranged to by pass the pump delivery back to the reservoir if the pressure rise in the pump becomes excessive.

in operation of the hydraulic unit described the electric motor will be driven continuously at high speed and the pump shaft 37 will be driven at a suitably reduced speed by virtue of the reduction gear 4. Liquid is induced into the pump and delivered at pressure port 18, the actual pressure of the liquid so delivered being dependent on the flow rate of liquid selected. Liquid flows at any instant when the control valve 39 is adjusted to require a movement of the motor piston 9. Whenever the control valve 39 is returned to a null position no delivery is required from the pump and its pressure will rise to a maximum moving the swash plate to an angle in which the stroke of the pistons is extremely small, being sufficient only to compensate for leakage from the pump to the reservoir. At this highest pressure within the range the accumulator piston 46 will be deflected to a substantial degree against the loading of the inert gas in the cylinder 41. When the control valve 39 is moved to require movement of the motor piston 9, a flow of high-pressure liquid is immediately available by virtue of highpressure liquid within the high-pressure accumulator cylinder 41. Thus initial movement of the piston 9 is effected by liquid delivered from the accumulator cylinder, the drop in pressure then enabling the swash plate of the pump to move into a position where stroke is given to the pistons and the pump delivers liquid at pressure. The whole reservoir and the inlet to the pump is maintained filled with liquid at low pressure as determined by the pressure of the low-pressure accumulator and therefore no make up pump is required to maintain the pump primed with liquid. Liquid can be lost from the unit described only through the positions where seals isolate liquid at pressure from the ambient atmosphere.

The invention may be used with any kind of pump having a rotary cylinder block and an adjustable cam member to adjust piston stroke and for example could be equally applied to a radial cylinder pump.

In the illustrated embodiment the two servo piston and cylinder units are spaced at equal distances from the swash plate tilt axis but it is within the scope of the present invention to arrange that these two units are unequally spaced from this tilt axis. In such a case the relative areas of the pistons of the two servo units would be arranged so that the second servo piston when acted on by pump delivery pressure could exert a greater torque on the swash plate than that exerted by the first servo piston.

I claim:

1. A variable stroke hydraulic pump comprising a rotary cylinder block, pump pistons extending from cylinders in the block to engage a cam member such that the pistons reciprocate during block rotation, a pair of servo piston and cylinder units arranged to act by hydraulic pressure oppositely on the cam for moving the cam in the sense to vary piston stroke, a hydraulic connection from the pump delivery extending directly to one servo piston, a hydraulic connection from the pump delivery extending to a pilot valve in the second servo piston and a spring acting on the pilot valve in opposition to the force developed by pump delivery pressure whereby the pilot valve assumes a position in accordance with pump delivery pressure to connect the pump delivery pressure or a lower pressure to act on the second servo piston to adjust the cam to a position in accordance with the position assumed by the pilot valve.

2. A variable stroke hydraulic pump as claimed in claim 1 wherein the cam is a swash plate.

3. A variable stroke hydraulic pump as claimed in claim 2 wherein the cylinders in the block are parallel to the block rotation axis.

4. A variable stroke hydraulic pump as claimed in claim 2 wherein both servo units are located at equal distances from the tilt axis of the swash plate and the area of the first servo piston is smaller than the area of the second servo piston.

5. A variable stroke hydraulic pump as claimed in claim 1 including a low pressure accumulator arranged to feed liquid at low pressure into the pump and a high-pressure accumulator adapted to receive liquid at high pressure from the pump.

6. A variable stroke hydraulic pump as claimed in claim 3 wherein both servo units are located at equal distances from the tilt axis of the swash plate and the area of the first servo piston is smaller than the area of the second servo piston.

7. A variable stroke hydraulic pump as claimed in claim 2 including a low-pressure accumulator arranged to feed liquid at low pressure into the pump and a high-pressure accumulator adapted to receive liquid at high pressure from the pump.

8. A variable stroke hydraulic pump as claimed in claim 3 including a low-pressure accumulator arranged to feed liquid at low pressure into the pump and a high-pressure accumulator adapted to receive liquid at high pressure from the pump.

9. A variable stroke hydraulic pump as claimed in claim 4 including a low-pressure accumulator arranged to feed liquid at low pressure into the pump and a high-pressure accumulator adapted to receive liquid at high pressure from the pump.

10. A variable stroke hydraulic pump as claimed in claim 6 including a low-pressure accumulator arranged to feed liquid at low pressure into the pump and a high-pressure accumulator adapted to receive liquid at high pressure from the pump.